This invention relates to a process for increasing the recovery of oil from oil-bearing earth formations. More particularly, the invention relates to a process for increasing oil recovery wherein an oil recovery enhancing fluid is introduced through an injection well into an oil-bearing earth formation and displaced through said formation toward a production well, and oil is recovered through said production well. Specifically, the present invention relates to a process for increasing oil recovery wherein the oil recovery enhancing fluid comprises surface active petroleum sulfonates.
Primary recovery techniques which rely upon natural forces to obtain oil from oil-bearing earth formations generally yield only a small proportion of the oil in the earth formation. It has been estimated that the oil obtained by primary recovery generally amounts to less than about 20% of the oil in place. Secondary recovery techniques, such as water flooding or steam injection, have been developed to increase the proportion of oil obtainable. While such techniques may result in increased recoveries, they typically still leave from 60 to 70% of the oil originally present in the formation. Further efforts by the art to improve oil recoveries have resulted in development of so-called tertiary recovery techniques. One promising tertiary technique involves introducing a slug of an oil recovery enhancing fluid comprising a surface active petroleum sulfonate through an injection well into an oil-bearing earth formation, displacing the slug through the formation toward a production well and recovering oil displaced from the earth formation by the fluid through the production well.
Although such methods may result in improved oil recoveries ranging up to 60% of the original oil in place, the usefulness of such methods is severely limited by their high cost. The expense of the surface active material used in forming the oil recovery enhancing fluid constitutes a large portion of the cost of such tertiary recovery methods.
Efforts to reduce the cost of such tertiary recovery techniques include attempts to produce the desired surface active materials in situ by injecting into the ground compounds which will react to form surface active substances. Examples of this approach are described in U.S. Pat. Nos. 3,392,782; 3,398,791; and 3,387,655. Unfortunately, the difficulties encountered in controlling the reactions involved render such methods less effective than desired.
It has also been proposed to sulfonate crude oil adjacent the well site to obtain surface active petroleum sulfonates which can be used to form oil recovery enhancing fluids; see U.S. Pat. No. 4,147,638. The procedure proposed in this patent relies on commercial sources of sulfonating agents and is still undesirably expensive.